Honeycomb structure body and method of designing the same

ABSTRACT

A honeycomb structure body has an inner side base section and an outer side base section having a cylindrical shape. Inner side cells are formed in the inner side base section at a constant cell density. Outer side cells are formed in the outer side base section. A cell density of the outer side cells varies a radius direction. The outer side cells are formed on the basis of a relational equation of y=a(x−b) n +c, where x is a distance on the outer side base section measured from a central point on a radial cross section, y indicates the number of the outer side cells per one cm 2  at the distance x, a is a negative constant, b is a radius of the inner periphery of the outer side base section, c is the number of the inner side cells per one cm 2 , and n is a degree.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of application Ser. No. 14/662,529, filedMar. 19, 2015, and is related to and claims priority from JapanesePatent Application No. 2014-58457 filed on Mar. 20, 2014, the contentsof each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the invention

The present invention relates to honeycomb structure bodies and methodsof designing honeycomb structure bodies

2. Description of the Related Art

There have been known and widely used honeycomb structure bodies used incatalyst converters mounted on exhaust gas purification systems formotor vehicles, capable of purifying exhaust gas emitted from internalcombustion engines such as diesel engines. Such a honeycomb structurebody is mounted on an inside of an exhaust gas pipe in an exhaust gaspurification system connected to an internal combustion engine in orderto purify exhaust gas. In general, a honeycomb structure body has anouter peripheral wall of a cylindrical shape, partition walls arrangedin a lattice shape in the inside of the outer peripheral wall. Inparticular, the partition walls are formed to be arranged in a latticeshape to form a plurality of cells along an axial direction of thehoneycomb structure body. That is, each of the cells is surrounded bythe partition walls. The cells are formed along an axial direction ofthe honeycomb structure body, and catalyst is supported in the cells.

Exhaust gas emitted from the internal combustion engine is dischargedoutside through the exhaust gas pipe. Because exhaust gas is a hightemperature gas, the catalyst supported in the honeycomb structure bodyis activated by heat energy of the exhaust gas. The honeycomb structurebody supporting activated catalyst of a high temperature purifies theexhaust gas when the exhaust gas passes through the cells formed in thehoneycomb structure body.

When the honeycomb structure body is divided into two sections, i.e. acentral section (as an inner section) and an outer side section viewedon a radial cross section of the honeycomb structure body, there is ingeneral a tendency that a large amount of exhaust gas passes through thecells arranged in the central section of the honeycomb structure bodywhen compared with an amount of exhaust gas passing through the cellsarranged in the outer side section of the honeycomb structure body in aradial cross section. Such a radial cross section of the honeycombstructure body is a cross section in a radial direction which isperpendicular to an axial direction or a longitudinal direction of thehoneycomb structure body.

For example, a patent document, Japanese patent laid open publicationNo. 2002-177794 has disclosed a honeycomb structure body having aconventional structure in which a radial cross section of the honeycombstructure body is divided into two sections, i.e. a central section (asan inner section) and an outer side section. In order to improve thepurification capability of exhaust gas, an amount of catalyst supportedin the central section is increased, and on the other hand, an amount ofcatalyst supported in the outer side section is decreased.

However, the honeycomb structure body disclosed in the patent documentpreviously described has a drawback as follows. The honeycomb structurebody disclosed in the patent document has the central section of thehoneycomb structure body in which a large amount of catalyst issupported in the cells of the central section in order to increase theexhaust gas purification capability of the central section as comparedwith that of the outer side section. However, this structure cannotsolve the conventional problem previously described, i.e. cannoteliminate a difference in flow amount between the central section andthe outer side section.

When such a difference in flow amount occurs between the central sectionand the outer side section, the central section becomes a hightemperature and the outer side section becomes a low temperature.Accordingly, the outer side section requires a long period of time untila temperature of the cells with catalyst formed in the outer sidesection reaches the catalyst activation temperature when compared withthe central section. Further, there is another possible problem that thecells of the outer side section cannot reach the activation temperatureto sufficiently activate the catalyst. This reduces the purificationcapability of the honeycomb structure body.

SUMMARY

It is therefore desired to provide a honeycomb structure body having animproved cell structure and a method of designing the honeycombstructure body capable of passing exhaust gas emitted from an internalcombustion engine through the overall cells at a constant flow speed,and purifying exhaust gas with high efficiency.

An exemplary embodiment provides a method of designing a honeycombstructure body having an inner side base section and an outer side basesection. The inner side base section has a cylindrical shape in which aplurality of inner side cells are formed and arranged at a first celldensity which is a constant value. The outer side base section has acylindrical shape, which is formed outside of the inner side basesection. In the outer side base section, a plurality of outer side cellsare formed to be arranged at a second cell density which varies in aradial direction which is perpendicular to an axial direction of thehoneycomb structure body. In particular, the method determines thenumber of the outer side cells to be formed in the outer side basesection on the basis of a relational equation of y=a(x−b)^(n)+c, where aindicates an optional negative constant which represents a change rateof the second cell density of the outer side cells formed in the outerside base section, b indicates a radius of the inner periphery of theouter side base section, c indicates the number of the inner side cellsper one cm² formed in the inner side base section, n indicates anoptional degree, x indicates a distance on the outer side base section,measured from a central point on a radial cross section which isperpendicular to an axial direction of the honeycomb structure body, andy indicates the number of the outer side cells, to be formed in theouter side base section, per one cm² at the distance x measured from thecentral point.

In accordance with another exemplary embodiment, there is provided ahoneycomb structure body having an inner side base section and an outerside base section. The inner side base section has a cylindrical shapein which a plurality of inner side cells are formed and arranged at afirst cell density of a constant value. The outer side base section hasa cylindrical shape, which is formed outside of the inner side basesection. In the outer side base section, a plurality of outer side cellsare formed and arranged at a second cell density which varies in aradial direction perpendicular to an axial direction of the honeycombstructure body. In addition, the outer side cells are formed in theouter side base section on the basis of a relational equation ofy=a(x−b)^(n)+c, where a indicates an optional negative constant whichrepresents a change rate of the second cell density of the outer sidecells formed in the outer side base section, b indicates a radius of theinner periphery of the outer side base section, c indicates the numberof the inner side cells per one cm² formed in the inner side basesection, n indicates an optional degree, x indicates a distance on theouter side base section, measured from a central point on a radial crosssection which is perpendicular to an axial direction of the honeycombstructure body, and y indicates the number of the outer side cells,formed in the outer side base section, per one cm² at the distance xmeasured from the central point.

The method of designing a honeycomb structure body provides therelational equation of y=a(x−b)^(n)+c. This makes it possible tocorrectly design an optimum structure of a honeycomb structure bodyhaving the inner side base section and the outer side base sectionthrough which exhaust gas can uniformly flows without any deviation ofexhaust gas flow. That is, the honeycomb structure body designed by themethod has a uniform distribution of flow speed of exhaust gas when theexhaust gas passes through the honeycomb structure body.

By the way, if overall cells are formed at a uniform cell density in ahoneycomb structure body, and exhaust gas passes through the cells,there is a tendency to delay a flow speed of exhaust gas in the cellsformed in an outer side section when compared with a flow speed of theexhaust gas in the cells formed in an inner side section which is nearthe central point of the honeycomb structure body. Further, there is atendency to increase a change rate in flow speed of exhaust gas in thecells of the outer side section, as compared with that in the cellsformed the inner side section.

After considering the problem previously described, the method accordingto the exemplary embodiment designs an improved structure of thehoneycomb structure body having the inner side base section and theouter side base section. In this structure, exhaust gas flows, i.e.passes through the overall cells at a high speed, in which a variationor a change rate of flow speed of exhaust gas is relatively small. Thatis, exhaust gas passes through the inner side cells in the inner sidebase section at a constant flow speed. Because the inner side basesection provides a uniform distribution of flow speed of exhaust gas, itis possible to form the inner side cells having a first cell density inthe inner side base section. The first cell density is a constant celldensity in which the inner side cells are uniformly arranged.

On the other hand, because exhaust gas passes through the outer sidecells in the outer side base section at a relatively low speed, ascompared with the flow speed of exhaust gas in the inner side cellsarranged in the inner side base section, exhaust gas has a large changerate of flow speed in the outer side base section, the outer side cellsare arranged at a second cell density which gradually decreases, i.e.varies from the inner periphery of the outer side base section to theoutermost periphery of the honeycomb structure body. That is, the secondcell density of the outer side cells formed in the outer side basesection is lower than the first cell density (which is a constant celldensity) of the inner side cells formed in the inner side base section.Furthermore, the method according to the exemplary embodiment designsthe honeycomb structure body so that the second cell density of theouter side cells is decreased gradually from the inner periphery of theouter side base section to the outermost periphery of the honeycombstructure body.

The above exemplary embodiment provides the relational equation ofy=a(x−b)^(n)+c . . . (E1) in order to produce the honeycomb structurebody having an improved structure and excellent purification capabilityof exhaust gas.

The following variables are optionally determined on the basis ofvarious parameters, for example, a shape of the exhaust gas pipe towhich the honeycomb structure body is applied:

-   -   Position of the inner periphery of the outer side base section;    -   Cell density of the inner side base section; and    -   Change rate of the cell density in the outer side base section.

Each of the values “a”, “b”, “c”, and “n” is an optional constant value.That is, it is possible to determine these optional constant values “a”,“b”, “c”, and “n” on the basis of various conditions to produce ahoneycomb structure body. As a result, it is possible to easily producethe honeycomb structure body having a uniform distribution in flow speedof exhaust gas by using the relational equation of y=a(x−b)^(n)+c, . . .(E1).

It is possible for the exemplary embodiment to provide the honeycombstructure body having a uniform distribution in temperature when exhaustgas passes through the overall cells in the honeycomb structure body,and increase a temperature of the overall cells uniformly to anactivation temperature of catalyst supported in the overall cellsarranged in the honeycomb structure body. This makes it possible for thehoneycomb structure body to have an excellent purification capability topurify exhaust gas emitted from an internal combustion engine with highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 is a view explaining a catalyst converter equipped with ahoneycomb structure body according to an exemplary embodiment of thepresent invention;

FIG. 2 is a view showing a partial cross section of the honeycombstructure body, along the line II-II shown in FIG. 1;

FIG. 3 is a graph showing experimental results of test samples obtainedby a first experimental test, which indicate a relationship between apurification rate (%) of exhaust gas and a degree “n” in a relationalequation of y=a(x−b)^(n)+c, when test samples were in a low load state;

FIG. 4 is a graph showing experimental results of test samples obtainedby the first experimental test, which indicate a relationship betweenthe purification rate (%) of exhaust gas and the degree “n” in therelational equation of y=a(x−b)^(n)+c, when the test samples were in ahigh load state;

FIG. 5 is a graph showing experimental results of test samples obtainedby a second experimental test, which indicates a relationship between aradius ratio and a distribution of flow speed of exhaust gas in the testsamples, where the radius ratio of each test sample indicates a ratio ofa distance measured from a central point P of each test sample to aradius of an upstream side pipe; and

FIG. 6 is a partial enlarged view of the graph shown in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription of the various embodiments, like reference characters ornumerals designate like or equivalent component parts throughout theseveral diagrams.

A description will be given of a honeycomb structure body and a methodof designing the honeycomb structure body according to preferredexemplary embodiments of the present invention.

It is preferable for the honeycomb structure body according to apreferred exemplary embodiment to have a structure which satisfies arelationship of −0.1<=a<=−0.01, where reference character “a” indicatesa constant value. Similarly, it is preferable for the design methodaccording to a preferred exemplary embodiment to design a structure of ahoneycomb structure body. The structure of the honeycomb structure bodydesigned by the method satisfies a relationship of −0.1<=a<=−0.01, wherereference character “a” indicates a constant value. This structure makesit possible to form cells having an optional cell density in an outerside base section by using an outer side base material. Further, thisstructure makes it possible to provide a uniform distribution of flowingexhaust gas in the honeycomb structure body. As a result, exhaust gascan flow in the entire cells at a uniform flow speed in the honeycombstructure body. This makes it possible to improve the purificationcapability of the honeycomb structure body.

On the other hand, when the constant value “a” is less than 0.1 (a<0.1),the number “y” of the cells calculated by relational equation (E1) ofy=a(x−b)^(n)+c becomes a negative value. This structure has a possibleproblem of it being difficult to correctly form the outer side basesection in a honeycomb structure body.

The important relational equation (E1) of y=a(x−b)^(n)+c will beexplained later in detail.

Further, it is preferable that the degree “n” used in the relationalequation (E1) is within a range of 0<n<2.43. This structure makes itpossible to improve the purification capability of purifying exhaust gaswhen the honeycomb structure body is in a low load state in which arelatively low flow amount of exhaust gas passes through the honeycombstructure body.

Still further, it is preferable that the degree “n” used in therelational equation (E1) is within a range of 0<n<2.41. In this case, inaddition to the feature obtained when the honeycomb structure body is ina low load state previously described, it is possible for the honeycombstructure body to further improve the purification capability ofpurifying exhaust gas when the honeycomb structure body is in a highload state in which a relatively high flow amount of exhaust gas passesthrough the honeycomb structure body.

Still further, it is preferable for the honeycomb structure bodyaccording to the present invention to have a structure which satisfies arelationship of 0.2 R<=b<=0.6 R, where reference character “R” indicatesa radius of an outer periphery of the honeycomb structure body, andreference character “b” indicates a radius of an inner periphery of theouter side base section.

A change of the flow speed of the exhaust gas becomes small in the areawhich satisfies that the radius “b” of the inner periphery of the outerside base section is within a range of b<0.2 R. Accordingly, in thisarea in the outer side base section of the honeycomb structure body, aflow speed of the exhaust gas has a uniform distribution.

In addition, a change of the flow speed of the exhaust gas becomes largein the area which satisfies that the radius “b” of the inner peripheryof the outer side base section is within a range of b>0.6 R.

Accordingly, it is possible to reliably form the outer side base sectionin an area in which a change of a flow speed of exhaust gas becomeslarge when the radius “b” of the inner periphery of the outer side basesection is within a range which satisfies the relationship of 0.2R<=b<=0.6 R. This structure makes it possible for the honeycombstructure body to have a uniform distribution of a flow speed of exhaustgas with high efficiency.

Exemplary Embodiment

A description will now be given of a honeycomb structure body 1according to an exemplary embodiment with reference to FIG. 1 and FIG.2.

FIG. 1 is a view explaining a catalyst converter 100 using the honeycombstructure body 1 according to the exemplary embodiment. FIG. 2 is a viewshowing a partial cross section of the honeycomb structure body 1 to beused in the catalyst converter 100, along the line II-II shown in FIG.1.

As shown in FIG. 1 and FIG. 2, the honeycomb structure body 1 accordingto the exemplary embodiment has a plurality of inner side cells 112 andouter side cells 122. That is, each of the inner side cells 112 and theouter side cells 122 is surrounded by partition walls to have a pipeshape formed extending in an axial direction of the honeycomb structurebody 1. Exhaust gas emitted from an internal combustion engine (notshown) flows in the inner side cells 112 and the outer side cells 122formed in the honeycomb structure body 1.

In particular, the cells 112 are formed in an inner side base section11. The inner side base section 11 has a same cell density. On the otherhand, the outer side cells 122 are formed in an outer side base section12. The outer side base section 12 has a cell density which is changedfrom a radial direction of the honeycomb structure body 1.

The outer side cells 122 are formed in the outer side base section 12 inthe honeycomb structure body 1 so that the number y of the outer sidecells 122 is calculated on the basis of the relational equation (E1):

y=a(x−b)^(n)c,  (E1),

where the reference character “x” indicates a distance measured from acentral point P on a radial cross section which is perpendicular to anaxial direction of the honeycomb structure body 1, and the referencecharacter “y” indicates the number of the outer side cells 122 in theouter side base section 12 per one cm² at the distance x measured fromthe central point P.

In the relational equation (E1) of y=a(x−b)^(n)c previously described,the reference character “a” indicates an optional negative constantwhich represents a change rate of a cell density, the referencecharacter “b” indicates a radius of the inner periphery 123 of the outerside base section 12, the reference character “c” indicates the numberof the inner side cells 112 per one cm² formed in the inner side basesection 11, and the reference character “n” indicates an optionaldegree.

A description will now be given of the structure of the honeycombstructure body 1 according to the exemplary embodiment.

As shown in FIG. 1, the honeycomb structure body 1 according to theexemplary embodiment is mounted on a motor vehicle equipped with aninternal combustion engine such as a diesel engine and a gasolineengine. The honeycomb structure body 1 purifies exhaust gas emitted fromsuch an internal combustion engine. In more detail, the honeycombstructure body 1 is arranged at the inside of an exhaust gas pipe 2which communicates with the internal combustion engine. The honeycombstructure body 1 and the exhaust gas pipe 2 form the catalyst converter100.

The exhaust gas pipe 2 is comprised of a catalyst support pipe 22, anupstream side pipe 21 and a downstream side pipe 23. The honeycombstructure body 1 is arranged in the inside of the catalyst support pipe22. In other words, the catalyst support pipe 22 accommodates thehoneycomb structure body 1. The upstream side pipe 21 is arranged at anupstream side of the catalyst support pipe 22. The upstream side pipe 21is close to the internal combustion engine at the upstream side ofexhaust gas. The downstream side pipe 23 is arranged at a downstreamside of the catalyst support pipe 22.

The catalyst support pipe 22 has an inner diameter which is larger thana diameter of the upstream side pipe 21 and a diameter of the downstreamside pipe 23. The honeycomb structure body 1 is arranged in an insidechamber of the catalyst support pipe 22. The catalyst support pipe 22has an upstream side corn section 24 and a downstream side corn section25. The upstream side corn section 24 is formed at an upstream side inthe catalyst support pipe 22. A diameter of the upstream side cornsection 24 gradually varies from the diameter of the upstream side pipe21 to the diameter of the catalyst support pipe 22. Further, thedownstream side corn section 25 is formed at a downstream side in thecatalyst support pipe 22. A diameter of the downstream side corn section25 gradually varies from the diameter of the catalyst support pipe 22 tothe diameter of the downstream side pipe 23.

As shown in FIG. 1, the upstream side pipe 21 has a cylindrical shape.An outer periphery of the upstream side pipe 21 near a connection nodebetween the upstream side pipe 21 and the upstream side corn section 24has a straight-line shape so that a central axial of the upstream sidepipe 21 and a central axis of the catalyst support pipe 22 form acoaxial axis. Similarly, an outer periphery of the downstream side pipe23 near a connection node between the downstream side pipe 23 and thedownstream side corn section 25 has a straight-line shape so that acentral axial of the downstream side pipe 23 and a central axis of thecatalyst support pipe 22 form a coaxial axis.

As shown in FIG. 1 and FIG. 2, the honeycomb structure body 1 accordingto the exemplary embodiment is comprised of a ceramic supporter andcatalyst. The catalyst is supported in the ceramic supporter and capableof purifying exhaust gas when exhaust gas passes through the honeycombstructure body 1 and in contact with the catalyst.

The ceramic supporter in the honeycomb structure body 1 is comprised ofinner side partition walls 111, outer side partition walls 121, theinner side cells 112 and the outer side cells 122. The inner sidepartition walls 111 and the outer side partition walls 121 are arrangedin a lattice shape. That is, each of the inner side cells 112 issurrounded by the inner side partition walls 111. Similarly, each of theouter side cells 122 is surrounded by the outer side partition walls121.

The honeycomb structure body 1 further has an outer peripheral wall 13having a cylindrical shape. The outer periphery is covered with theouter peripheral wall 13. That is, in the structure of the honeycombstructure body 1 according to the exemplary embodiment, an outermostperiphery 131 of the honeycomb structure body 1 has a diameter R of 51.5mm.

As shown in FIG. 2, the honeycomb structure body 1 has the inner sidebase section 11 and the outer side base section 12. The inner side basesection 11 is formed a radially inner side in a radial cross section ofthe honeycomb structure body 1. On the other hand, the outer side basesection 12 is formed a radially outer side in the radial cross sectionof the honeycomb structure body 1. The inner side base section 11 isarranged adjacently to the outer side base section 12. That is, theouter side base section 12 is formed between the outer periphery of theinner side base section 11 and the outermost periphery 131 of thehoneycomb structure body 1.

The inner side base section 11 has a cylindrical shape or a columnarshape. The inner side base section 11 has a plurality of the inner sidepartition walls 111 arranged in a lattice shape and a plurality of theinner side cells 112. Each of the inner side cells 112 are surrounded bythe inner side partition walls 111. The inner side cells 112 are formedin a longitudinal direction, i.e. an axial direction of the honeycombstructure body 1. In particular, each of the inner side cells 112 has aradial cross section having a hexagonal shape. The inner side cells 112are arranged at a same cell density in the inner side base section 11.In the structure of the honeycomb structure body 1 according to theexemplary embodiment, the inner side base section 11 has a first celldensity in which the number of the inner side cells 112 per one cm² is116. That is, the n umber c of the inner side cells 112 in the innerside base section 11 is a value of 116 (c=116).

The outer side base section 12 has a cylindrical shape or a columnarshape. The inner side base section 11 is formed in the innercircumference side of the outer side base section 12.

The outer side base section 12 has a plurality of the outer sidepartition walls 121 arranged in a lattice shape and a plurality of theouter side cells 122. Each of the outer side cells 122 are surrounded bythe outer side partition walls 121. Similar to the inner side cells 112,the outer side cells 122 are formed in a longitudinal direction, i.e. anaxial direction of the honeycomb structure body 1. In particular, eachof the outer side cells 122 has a radial cross section having ahexagonal shape.

In the structure of the honeycomb structure body 1 according to theexemplary embodiment, an innermost periphery 123 of the outer side basesection 12 has a radius “b” of 20 mm (b=20 mm).

When a flow passage of the upstream side pipe 21 has a diameter R1, thefollowing relationship is satisfied:

b=0.39 R1,

where b indicates a radius of the innermost periphery 123 of the outerside base section 12.

The method according to the exemplary embodiment designs the outer sidebase section 12 in the honeycomb structure body 1 on the basis of therelational equation (E1) of y=a(x−b)^(n)c. In this relational equation(E1), reference character “a” indicates an optional negative constantwhich represents a change rate of a cell density in the outer side basesection 12, and reference character “n” indicates an optional degree. Inthe exemplary embodiment, a=−0.046, and n=2. Further, as previouslydescribed, the innermost periphery 123 of the outer side base section 12has a radius b of 20 (b=20), and the number of the inner side cells 112per one cm², formed in the inner side base section 11 is 116 (c=116).When the values a, b, c and n are inputted into the relational equation(e1), the following relational equation (E2) is obtained.

y=−0.046 (x−20)²+116,  (E2).

When the distance “x” measured from the central point P is inserted intothe equation (E2), the number “y” of the cells per one cm² at thedistance x is obtained. The distance “x” is present between theinnermost periphery 123 of the outer side base section 12 and theoutermost periphery of the outer side base section 12. That is, thefollowing result is obtained:

20 <=x<=51.5.

In particular, the number “y” of the cells outer side cells 122 in theouter side partition walls 121 is sequentially changed on the basis ofthe distance “x” so that the cell density of the outer side cells 122 isdecreased from the inner circumference side to the outer circumferenceside of the outer side base section 12.

By the way, the method according to the exemplary embodiment produces ametal die having a structure which corresponds to the specific structureof the cell arrangement of the inner side sells 112 and the outer sidecells 122 in the honeycomb structure body 1.

For example, a manufacturing method produces the honeycomb structurebody 1 by using the metal dies having the specific structure which hasbeen designed by the method according to the exemplary embodimentpreviously described.

The manufacturing method produces prepares ceramic raw material, andadds water, binder, etc. to the prepared ceramic raw material, and mixesit to produce a mixture.

The manufacturing method extrudes the mixture by using an extrusionmetal die to produce a honeycomb structure molded body. The metal dieproduced by the design method according to the exemplary embodiment hasa cross section having a pattern of slit grooves which correspond to thearrangement of the inner side cells 112 and the outer side cells 122 ofthe honeycomb structure body 1.

The manufacturing method dries the honeycomb structure molded body byusing microwaves. After the drying step, the manufacturing method cutsthe dried honeycomb structure body to a plurality of parts having adesired length. After this, the manufacturing method fires the honeycombstructure body having the desired length at a predetermined temperatureto produce the honeycomb structure body 1.

A description will now be given of the action and effects of thehoneycomb structure body 1 and the design method of designing thehoneycomb structure body 1 according to the exemplary embodiment.

The design method of designing the structure of the honeycomb structurebody 1 according to the exemplary embodiment provides the relationalequation (E1) and the other various relationships in order to correctlydetermine an optimum structure of the inner side base section 11 havingthe inner side cells 112 and the outer side base section 12 having theouter side cells 122 in the honeycomb structure body 1. This makes itpossible to design and produce the honeycomb structure body 1 having auniform gas-flow speed distribution capable of passing exhaust gasthrough the overall cells at a uniform flow speed. That is, exhaust gascan flow at a constant flow speed in the entire cells formed in thehoneycomb structure body 1.

If a honeycomb structure has a uniform cell density, there is a tendencyto more delay a flow speed of exhaust gas in an outer side when comparedwith a flow speed of exhaust gas in an inner side which is near thecentral point of the honeycomb structure body. Further, there is atendency to increase a change rate of flow speed of exhaust gas at theouter side, when compared with a change rate of flow speed in the innerside, which is near the central point in a radial cross section which isperpendicular to an axial direction of the honeycomb structure body.

The method according to the exemplary embodiment considers andeliminates this tendency caused when the overall cells are formed in auniform cell density, and provides the improved structure comprised ofthe inner side base section 11 and the outer side base section 12 in thehoneycomb structure body 1.

In general, exhaust gas passes through the cells at a high speed, and avariation or a change rate of flow speed of exhaust gas is relativelysmall. That is, exhaust gas passes through the cells formed and arrangedin the inner side base section 11 at a constant flow speed. Because theinner side base section 11 has a uniform distribution of flow speed ofexhaust gas, it is possible form the inner side base section 11 to havea first cell density which is a constant cell density in which the innerside cells 112 are uniformly arranged to have a constant cell density.

On the other hand, because exhaust gas passes through at a relativelylow speed, as compared with the flow speed of exhaust gas in the innerside base section 11, exhaust gas has a large change rate of flow speedin the outer side base section 12, the outer side cells 122 has a secondcell density which gradually decreases, i.e. varies from the innerperiphery 123 of the outer side base section 12 to the outermostperiphery 131 of the honeycomb structure body 1. That is, the secondcell density of the outer side cells 122 formed in the outer side basesection 12 is lower than the first cell density (which is a constantcell density) of the inner side cells 112 formed in the inner side basesection 11. Furthermore, the design method according to the exemplaryembodiment designs that the second cell density of the outer side cells122 is decreased gradually from the inner periphery 123 of the outerside base section 12 to the outermost periphery 131 of the honeycombstructure body 1.

The exemplary embodiment provides the relational equation ofy=a(x−b)^(n)+c . . . (E1) in order to produce the honeycomb structurebody 1 having a specific structure.

The following parameters (a), (b) and (c) are optionally determined onthe basis of various condition, for example, a shape of the exhaust gaspipe to which the honeycomb structure body 1:

-   -   (a) Position of the inner periphery 123 of the outer side base        section 12;    -   (b) Cell density of the inner side base section 11; and    -   (c) Change rate of the cell density in the outer side base        section 12.

Each of the values “a”, “b”, “c”, and “n” is an optional constant value.That is, it is possible to determine these optional constant values “a”,“b”, “c”, and “n” on the basis of various conditions to produce ahoneycomb structure body.

As a result, it is possible to easily produce the honeycomb structurebody 1 having a uniform distribution in flow speed of exhaust gas byusing the relational equation of y=a(x−b)^(n)+c, . . . (E1).

It is possible for the exemplary embodiment to provide the honeycombstructure body 1 having a uniform gas-flow speed distribution intemperature when exhaust gas passes through the honeycomb structure body1, and uniformly increases a temperature of the overall cells of thehoneycomb structure body 1 to an activation temperature of catalystsupported in the honeycomb structure body 1. This makes it possible forthe honeycomb structure body 1 to purify exhaust gas emitted from aninternal combustion engine with high efficiency.

In addition, when the honeycomb structure body 1 according to theexemplary embodiment is produced, the constant “a” is within a range of−0.1<=a<=−0.01 in the relational equation of y=a(x−b)^(n)+c, . . . (E1).This makes it possible to form the outer side cells 122 at an optimumcell density in an outer side base section 12. This makes it alsopossible to provide a uniform distribution in flow speed of exhaust gasin the overall cells of the honeycomb structure body 1, and improve thepurification capability thereof.

Further, when the honeycomb structure body 1 according to the exemplaryembodiment is produced, the degree “n” is within a range of 0<n<2.41 inthe relational equation of y=a(x−b)^(n)+c, . . . (E1). This makes itpossible for the honeycomb structure body 1 to provide improvedpurification capability of purifying exhaust gas even if the honeycombstructure body 1 is in a high load, i.e. a large amount of exhaust gaspasses through the honeycomb structure body 1.

Still further, when the honeycomb structure body 1 according to theexemplary embodiment is produced, the following relationship issatisfied in the relational equation (E1): 0.2 R<=b<=0.6 R, wherereference character “R” indicates a radius of an outer periphery of thehoneycomb structure body 1, and reference character “b” indicates aradius of the inner periphery 123 of the outer side base section 12.This makes it possible to reliably and correctly form the outer sidebase section 12 within an area in which exhaust gas has a large changerate of its flow speed. In addition. it is possible to produce thehoneycomb structure body 1 with a uniform distribution of flow speed ofexhaust gas.

Still further, the honeycomb structure body 1 according to the exemplaryembodiment has the improved structure previously described. That is, theouter side base section 12 is formed between the outer periphery of theinner side base section 11 and the outermost periphery 131 of thehoneycomb structure body 1. Because the outer peripheral side of thehoneycomb structure body 1 is formed in the outer side base section 12in which exhaust gas has a high change rate of its flow speed, thisstructure makes it possible for the honeycomb structure body 1 have auniform distribution of flow speed of exhaust gas and to flow exhaustgas uniformly in the overall cells in the honeycomb structure body 1with high efficiency.

As previously described in detail, it is possible for the design methodaccording to the exemplary embodiment to design an improved structure ofthe honeycomb structure body 1 having a uniform gas-flow speeddistribution. This structure makes it possible for exhaust gas to flowuniformly in the overall cells in the honeycomb structure body 1 withhigh efficiency.

First Experimental Test

A description will now be given of a first experimental test to detectthe purification capability of test samples as honeycomb structurebodies having various degrees “n”.

The test samples were produced on the basis of the relational equationof y=−0.046 (x−20)^(n)+116, where a=−0.046, b=20, and c=116 in therelational equation (E1) of y=a(x−b)^(n)+c.

The first experimental test gradually increased the degree “n” from zeroin order to produce the test samples. Other components of the testsamples are the same of those of the honeycomb structure body 1according to the exemplary embodiment previously described.

FIG. 3 is a graph showing experimental results of test samples obtainedby the first experimental test. That is, the graph shown in FIG. 3indicates a relationship between a purification rate (%) of exhaust gasand the degree “n” in the relational equation (E1) of y=a(x−b)^(n)+cwhen the test samples were in a low load state. FIG. 4 is a graphshowing experimental results of test samples obtained by the firstexperimental test. That is, the graph shown in FIG. 4 indicates arelationship between the purification rate (%) of exhaust gas and thedegree “n” in the relational equation of y=a(x−b)^(n)+c, . . . (E1) whenthe test samples were in a high load state.

In FIG. 3 and FIG. 4, vertical axis indicates the purification rate (%)of exhaust gas, and horizontal axis indicates the degree “n” in therelational equation of y=a(x−b)^(n)+c, . . . (E1).

The curve L1 in FIG. 3 indicates the relationship between thepurification rate (%) of exhaust gas and the degree “n” in therelational equation of y=a(x−b)^(n)+c, . . . (E1) when exhaust gasintroduced into the test sample has a flow amount of 20 (g/s) and atemperature of 500° C. The dotted line B1 shown in FIG. 3 indicates apurification rate (%) of exhaust gas when cells were formed at aconstant cell density (116 cells/cm²) in the test samples.

The curve L2 in FIG. 4 indicates the relationship between thepurification rate (%) of exhaust gas and the degree “n” in therelational equation of y=a(x−b)^(n)+c, . . . (E1) when exhaust gasintroduced into the test samples has a flow amount of 60 (g/s) and atemperature of 800° C. The dotted line B2 in FIG. 4 indicates apurification rate (%) of exhaust gas when the cells were formed at theconstant cell density (116 cells/cm²) in the test samples.

As shown in FIG. 3, when the degree “n” is 0 (n=0), the test sample asthe honeycomb structure body has a purification rate which isapproximately equal to the purification rate of the test sample(indicated by the dotted line B1) having the same cell density.

The more the degree “n” gradually increases from zero (n=0), the morethe purification rate of the test samples gradually increases. Forexample, when the degree “n” is 2.25 (n=2.25), the test sample has themaximum purification rate. When the degree “n” exceeds 2.25 (n>2.25),the purification rate of the test samples is drastically decreased.

When the degree “n” is not less than 2.43 (n>=2.43), the purificationrate of the test samples is lower than that of the test sample indicatedby the dotted line B1. That is, it can be understood from theexperimental results shown in FIG. 3, as compared with the test samplein which the cells (i.e. the cells 112 and the cells 122) are formed atthe same cell density indicated by the dotted line B1, the honeycombstructure body has an excellent purification rate capable of purifyingexhaust gas as long as the degree “n” is within a range of 0<n<2.43 evenif the test sample is in a low load state.

As shown in FIG. 4, when the degree “n” is 0 (n=0), the test sample asthe honeycomb structure body has a purification rate which isapproximately equal to the purification rate of the test sample(indicated by the dotted line B2) having the same cell density.

The more the degree “n” gradually increases from zero (n=0), the morethe purification rate of the test samples gradually increases. Forexample, when the degree “n” is 2 (n=2), the test sample has the maximumpurification rate. When the degree “n” exceeds 2 (n>2), the purificationrate of the test samples is drastically decreased.

When the degree “n” is not less than 2.41 (n>=2.41), the purificationrate of the test samples is lower than that of the test sample indicatedby the dotted line B2. That is, it can be understood from theexperimental results shown in FIG. 4, as compared with the test sample,in which the cells (i.e. the cells 111 and the cells 112) are formed atthe same cell density, indicated by the dotted line B2, the honeycombstructure body has an excellent purification rate capable of purifyingexhaust gas as long as the degree “n” is within a range of 0<n<2.41 evenif the test sample is in a high load state.

Second Experimental Test

A description will now be given of a second experimental test to detecta distribution of flow speed (m/s) of exhaust gas in test samples ashoneycomb structure bodies.

FIG. 5 is a graph showing experimental results of test samples obtainedby the second experimental test. That is, the graph shown in FIG. 5indicates a relationship between a radius ratio (x/R1) and adistribution of flow speed (m/s) of exhaust gas in the test samples.FIG. 6 is a partial enlarged view of the graph shown in FIG. 5.

In FIG. 5 and FIG. 6, the vertical axis indicates a flow speed (m/s) ofexhaust gas which passes through each test sample, and the horizontalaxis indicates the radius ratio (x/R1). In more detail, each test sampleis a honeycomb structure body having a structure in which cells areformed at a constant cell density and the test samples have the samecell density. In FIG. 5, the radius ratio (x/R1) indicates a ratio of adistance “x” measured from a central point “P” to a radius “R1” of anupstream side pipe. This upstream side pipe corresponds to the upstreamside pipe 21 shown in FIG. 1. In particular, the curves L3 and L4 shownin FIG. 5 and FIG. 6 indicate two groups of the test samples having asame cell density (116 cells per cm²) and different lengths (L3: 130 mm,L4: 105 mm). The curves L5 and L6 shown in FIG. 5 and FIG. 6 indicatetwo groups of the test samples having a same cell density (93 cells percm²) and different lengths (L5: 130 mm, L6: 105 mm).

That is, the curve L3 shown in FIG. 5 and FIG. 6 indicates the group ofthe test samples (as honeycomb structure bodies) having cells formed atthe cell density of 116 cells/cm² and the length of 130 mm. The curve L4shown in FIG. 5 and FIG. 6 indicates the group of the test samples (ashoneycomb structure bodies) having cells formed at the cell density of116 cells/cm² and the length of 105 mm. The curve L5 shown in FIG. 5 andFIG. 6 indicates the group of the test samples (as honeycomb structurebodies) having cells formed at the cell density of 93 cells/cm² and thelength of 130 mm. The curve L6 shown in FIG. 5 and FIG. 6 indicates thegroup of the test samples (as honeycomb structure bodies) having cellsformed at the cell density of 93 cells/cm² and the length of 105 mm.Other components of the test samples used in the second experimentaltest are the same of those of the honeycomb structure body 1 accordingto the exemplary embodiment previously described.

As shown in FIG. 5 and FIG. 6, as compared with a flow speed of exhaustgas passing through a central area around the central point P of eachtest sample (honeycomb structure body), when the radius ratio (x/R1) isless than 0.2 in each of the curves L3 to L6, a change rate of flowspeed of exhaust gas is extremely small. It can be recognized that aninflection point of flow speed of exhaust gas is detected in the testsample having the radius ratio of 0.2.

In addition, it can be recognized that a change rate of flow speed ofexhaust gas increases in the test samples having a radius ratio of morethan 0.6.

Accordingly, it is possible to provide a honeycomb structure body havingan improved structure in which the outer side base section is reliablyformed from a first formation area to a second formation area. That is,in the first formation area, exhaust gas passes through at a relativelylow flow speed. In the second formation area, exhaust gas passes throughat a high flow speed when the honeycomb structure body satisfies therelationship of 0.2 R<=b<=0.6 R, where reference character “R” indicatesa radius of the outer periphery of the honeycomb structure body, andreference character “b” indicates a radius of the inner periphery of theouter side base section in the honeycomb structure body.

While specific embodiments of the present invention have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limited to the scope of the present inventionwhich is to be given the full breadth of the following claims and allequivalents thereof.

What is claimed is:
 1. A method of designing a honeycomb structure bodycomprising: steps of: designing an inner side base section having acylindrical shape in which a plurality of inner side cells are formedand arranged at a first cell density of a constant value; and designingan outer side base section having a cylindrical shape, formed outside ofthe inner side base section, in which a plurality of outer side cellsare formed to be arranged at a second cell density which varies in aradial direction which is perpendicular to an axial direction of thehoneycomb structure body, wherein the step of designing the outer sidebase section determines: the number of the outer side cells to be formedin the outer side base section on the basis of a relational equation ofy=a(x−b)^(n)+c, where a indicates an optional negative constant whichrepresents a change rate of the second cell density of the outer sidecells formed in the outer side base section, b indicates a radius of theinner periphery of the outer side base section, c indicates the numberof the inner side cells per one cm² formed in the inner side basesection, n indicates an optional degree, x indicates a distance on theouter side base section, measured from a central point on a radial crosssection which is perpendicular to an axial direction of the honeycombstructure body, and y indicates the number of the outer side cells, tobe formed in the outer side base section, per one cm² at the distance xmeasured from the central point.
 2. The method according to claim 1,wherein the step of designing the outer side base section designs thehoneycomb structure body so that the degree n in the relational equationof y=a(x−b)^(n)+c satisfies a relationship of 0<n<2.43.
 3. The methodaccording to claim 1, wherein the step of designing the outer side basesection designs the honeycomb structure body so that the degree n in therelational equation of y=a(x−b)^(n)+c satisfies a relationship of0<n<2.41.
 4. The method according to claim 1, wherein the step ofdesigning the outer side base section designs the honeycomb structurebody to satisfy a relationship of 0.2 R<=b<=0.6 R, where R indicates aradius of an outer periphery of the honeycomb structure body, and bindicates a radius of an inner periphery of the outer side base section.5. The method according to claim 1, wherein the step of designing theouter side base section designs the honeycomb structure body so that theouter side base section is formed between an outer periphery of theinner side base section and an outermost periphery of the honeycombstructure body.